The process for fermentation production of chemical substances using sugars as raw materials has been used to produce various industrial raw materials. Currently, as sugars to be used as fermentation raw materials, those derived from food materials such as sugar cane and sugar beets are industrially used. However, in view of the fact that a rise in the prices of food raw materials is expected due to future increase in the world population, or in an ethical view of the fact that sugars as industrial materials may compete with sugars for food, it has been a future issue to construct a process of efficiently producing a sugar liquid from a renewable nonfood resource, that is, cellulose-containing biomass, or a process of using the obtained sugar liquid as a fermentation raw material to thereby efficiently convert the obtained sugar liquid to an industrial raw material.
Cellulose-containing biomass are mainly composed of lignin which is an aromatic based polymer product, and cellulose or hemicellulose which are polymer products of monosaccharides. As a representative example of the process of producing a sugar liquid from cellulose-containing biomass, there is an acid treatment in which the cellulose-containing biomass is treated with dilute sulfuric acid. This treatment is a technique that a cellulose fraction is separated from a dilute sulfuric acid-treated liquid containing xylose which is a pentose and the cellulose fraction is further subjected to an enzyme treatment to obtain glucose which is a hexose (A. Aden et al., “Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co-Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover,” NREL Technical Report (2002)). It has been advancing to scale-up and is said to be a method close to practical use. However, the separation of xylose from sulfuric acid is required for use of the xylose obtained by the dilute sulfuric acid treatment method as a fermentation raw material. In that case, the sulfuric acid is precipitated in a form of calcium sulfate and therefore the cost for waste material and cost involved in reducing environmental load come to be indispensable, which leaves cost reduction as a problem (Journal of Japan Society of Energy and Resources, Vol. 30, No. 5 and AIST TODAY, July Issue, 2009).
For such a problem of reducing the cost of treating sulfuric acid, examples include recovery of sulfuric acid. With regard to the recovery of sulfuric acid, there is disclosed, for example, a method of recovering sulfuric acid from sulfate by electrodialysis with using a bipolar membrane and a cation exchange membrane (Japanese Patent Application Laid-Open Publication No. 5-58601) and a method of employing an anion selective membrane and stripping hydrogen sulfide (Japanese Translation of PCT International Application Publication No. 2008-529946).
When sulfuric acid is recovered from a dilute sulfuric acid-treated liquid containing cellulose-containing biomass according to conventional techniques, there have been problems in that the cost of electricity and expenses for membranes consumed are high; and further the efficiency of recovering sulfuric acid is poor when the concentration of sulfuric acid is low. Therefore, it could be helpful to efficiently recover sulfuric acid in a sugar liquid production process by a dilute sulfuric acid treatment of cellulose-containing biomass.